Just match the revs. In other words make it as smooth as possible.
You want to have the rpms at where they would be at that moment if you were in the gear you are shifting too. That make sense? If there is a passenger in the car with you, with a good down shift, they would not be able to tell you down shifted other than from maybe the sound the engine makes. Just blip the gas to get the rpms where you want them to be and down shift. I know it sounds easier than it is but that is basically it.